1. Field of the Invention
The present invention relates to an image pickup apparatus and a system utilizing the same, and more particularly to an image pickup apparatus and a system such as a digital camera, a video camera, a copying apparatus, and a facsimile apparatus.
2. Background of the Invention
A solid-state image pickup apparatus formed by a one- or two-dimensional array of photoelectric conversion elements such as photodiodes is widely employed in a digital camera, a video camera, a copying apparatus, a facsimile apparatus and the like. The solid-state image pickup apparatus includes a CCD image pickup device and an amplifying solid-state image pickup apparatus represented by a CMOS sensor which is formed integrally with peripheral circuits by a CMOS process.
Such solid-state image pickup apparatus shows a trend toward a larger number of pixels, with a decrease in the area of a photodiode, as a result of a reduction in the area of a pixel. It is therefore required to handle a signal charge of a smaller amount, and it is therefore required to reduce a dark current constituting a noise component, and to increase an effective area of the photodiode. For such purpose, EP 1017106A1 discloses in FIG. 4 (corresponding to Japanese Patent Application Laid-open No. 2000-232216) a configuration in which floating diffusion regions formed for every pixels are connected by a conductor, and in which the signal reading is executed by an amplification by a common amplifying MOS transistor, thereby reducing a number of transistors per unit pixel and maintaining the area of the photodiode larger.
Also when the solid-state image pickup apparatus becomes larger in the area, it becomes necessary, as disclosed in Japanese Patent Application Laid-open No. 2001-332714 (FIGS. 7 and 10) or Japanese Patent Application Laid-open No. 2001-230400 (FIGS. 1 and 16, corresponding to US 2001-1012133A) to form a well contact in order to obtain a firm substrate potential for the photodiode and the transistor and to suppress a shading phenomenon.
Also a fine structuring of the MOS transistors is essential in the image pickup device or in the peripheral circuits, there is widely employed a transistor having so-called LDD (lightly doped drain) structure.
In the aforementioned image pickup apparatus, in case of forming a well contact between the photodiodes, a element isolation region is formed for a device isolation between the well contact and the photodiode. Then a conductive layer for example of polysilicon is formed thereon, and a side wall may be formed in such conductive layer, in relation to the preparation of a transistor of an LDD structure.
The present invention has found a drawback of an increased dark current of the photodiode, depending on the arrangement of the side wall.